Impulse voltage generators can be used to test high-voltage components, such as power transformers. An impulse voltage generator can produce a voltage pulse which is supplied by suitable electrical circuitry from the impulse voltage generator to a component, such as a high voltage winding of the unit under test that is to be tested. A voltage pulse normally has a time duration in a range up to several tens of microseconds, and the maximum voltage—depending on the unit under test—is up to several mega volts (MV). Conclusions about the state of the tested component can be derived from a continuous measurement of current and/or voltage values within the electrical circuitry of the test layout when under the influence of the voltage pulse. For example, the age or a fault in the electrical insulation can be determined from the current and/or voltage measurements.
An impulse voltage generator has multiple capacitors which can be charged and connected in parallel to produce a high-voltage pulse. The capacitors can then be discharged, and electrically connected in series. Higher voltages can be achieved by the series connection. The impulse voltage generator can include a tower-like structure having a capacitor, a resistor, a spark gap, and insulators that are arranged in a grid structure. The insulators can be in the form of tubes composed of an insulation material, such as GRP (glass reinforced plastic) for example. The insulators can be arranged one behind the other along the tower-like structure, in a plurality of supporting columns which extend over the entire length of the structure. The electrical components can be arranged transversely with respect to the insulators. Impulse voltage generators should be operated only in the vertical, upright state, to maintain the necessary isolation separations from the adjacent ground potential. The highest voltage occurs at the tip of the impulse voltage generator.
High-voltage components such as power transformers can be very heavy, such as on the order of several hundred tons, depending on the electrical rating. Transportation of a power transformer stored within an electrical power distribution system to a fixed-installed test field, so that the transformer can be tested using an impulse voltage test for maintenance or for diagnostic purposes, is virtually impossible because of the high transportation cost. Furthermore, it is extremely rare for sufficient redundancy to be available in a power distribution network to allow a transformer to be removed without adversely affecting network operation.
For this reason, impulse voltage tests on power transformers are generally carried out in an original location without transporting. The test arrangement with the impulse voltage generator and further components required for the test, such as voltage dividers, measurement apparatuses and evaluation apparatuses, are transported in a plurality of assemblies to the testing or servicing location, and are assembled there to form a test arrangement. The voltage divider can be used to measure high voltages up to 2 MV, for example, as desired. The voltage divider can be of considerable size, such as at a height of 10 m, for example, in addition to the impulse voltage generator.
In some test circuit configurations for impulse voltage tests, a surge arrester can be provided. The surge arrester can cut off the impulse voltage when the rising impulse voltage pulse exceeds a specified threshold magnitude. Surge arresters can be installed in the respective test arrangement as separate components, and can be arranged as a column and at a considerable height.
The foregoing test circuits as described, are assembled on site which involves a considerable amount of time. In particular, the positioning and assembly of an impulse voltage generator, a surge arrester or a voltage divider can be time-consuming.